At present many information appliance products such as plasma TV and liquid crystal display, aside from various electronic circuits, have a power supply device to support the information appliances. The power supply device generally provides only low voltage electric power. Refer to FIG. 1 for a conventional power supply for the back light panel of a liquid crystal display. The back light panel includes cold cathode fluorescent lamps (CCFLs) that require a high voltage (as high as hundred or even thousand volts) to activate.
Namely, input alternating current (AC) voltage is transformed by a medium voltage rectification unit to become medium voltage direct current (DC) to be output. And the medium voltage DC is further transformed by a conversion unit to become low voltage DC to be output. The low voltage DC is processed by a voltage boosting unit (inverter) to output high voltage AC. The high voltage AC may drive the CCFLs. The efficiency of the voltage boosting unit is 80%. When the conversion unit at the previous stage also has efficiency of 80%, total efficiency (the voltage delivered to the CCFLs) is 80%×80%=64%.
As a large size liquid crystal display could use up to 20 lamp tubes, and each lamp tube has energy loss of 5W-10W, total energy loss could reach 36W to 72W. Thus the power supply device for the information appliances incurs a lot of power loss. Performance also cannot be improved.